In this paper we generalize
classical results in Diophantine approximation to the setting of an arbitrary numher
field in the context of the ring of S-integers. Specifically, we present theorems
pertaining to simultaneous approximations of linear forms and develop the notion of
badly approximable S-systems. In addition, we expand the subject of the geometry of
numbers over the adèle ring of a number field by developing the concept of the
adelic polar body. This theory is then used to produce transference theorems in this
general situation.